In 1928 Walter Garstang hypothesized that tunicates resemble the ancestral stock of the vertebrates. Explain this hypothesis.

Most scientists believed that the tadpole larvae of tunicates was a descendant of an free-swimming chordate ancestor. Walter Garstang of England suggested that the chordates were derived by retaining the larval form of sessile tunicate-like animals into adulthood. The tadpole larva of tunicates does bear all the right attributes to qualify as a possible vertebrate ancestor; notochord, hollow dorsal nerve chord, pharyngeal slits, endostyle, and postanal tail.

At some point, Garstang suggested, the tadpole larva failed to metamorphose into an adult tunicate, instead developing gonads and reproducing in the larval stage. With continued evolution, a new group of free-swimming animals appeared, the ancestors of cephalochordates and vertebrates. Garstang called this process paedomorphosis, a term describing the evolutionary retention of juvenile or larval traits in the adult body. He suggested that evolution may occur in larval stages of animals. In this case it led to the development of vertebrates.